Dragons are primordial beings created by a race of thought beings, the Fain, and the Earth spirit, Gaia. They are made from clay and have sparks of fire within them. When they die, they shed their fire through a tear and their bodies return to clay.
A dragon's eyes are jewel-like, and usually violet or amber. Dragon bodies are covered in sharp spines called stigs, which can be moved and shed at will. Their nostrils are wide, trumpet-like, and flared. All dragons have a triangular scale at the tip of the tail, called the isoscele, which is thought to have magical properties.
There are two kinds of dragons: the Pennykettle Dragons, little clay dragons created by Elizabeth Pennykettle with Icefire, and the Natural Dragons, those created by Gaia and the Fain. There are also Firebirds, bird-like creatures related to dragons (and can become dragonets), and Darklings, which are essentially inversions of dragons.
The most notable dragons include Gadzooks the Writing Dragon, and Gawain, last of the Natural Dragons. Dragons from the Last Dragon Chronicles shouldn't be confused with dragons from the Erth Dragons series.
Interesting fact: Dragons have a mechanism to end their life when they are useless, which works when they are really upset. This seems to have a use, as useless dragons can intentinally (maybe) cry out their life and this life can be used by Earth to create a more useful dragon being. This can be seen in first book, The fire Within, where David abandons their special writing dragon, Gadzooks, and they are crying out their life, luckily, David was nearby to catch the firetear (Dragon spark in a tear) and blow the life into a dragon.